单选题In an internal combustion engine, which of the devices listed will force the compression rings to seal the compression gases in the space above the piston?（）A Used of bimetallic piston ringsB Ring gap pre-tensioningC Thermal increase in ring-end cleara

A. Proxy

B. Load balancer

C. Router

D. Bandwidth shaper

What is a requirement for remote manual shutdown stations for internal combustion engine driven cargo pumps on tank barges ________．

A.They must be conspicuously marked

B.They must be located at least 10 feet from the engine

C.There must be at least two such shutdown devices

D.The valve rods shall be fitted with stuffing boxes

第一组： The Wartsila 50DF operates on the lean-bum principle: the mixture of air and gas in the cylinder has more air than is needed for complete combustion. Lean combustion reduces peak temperatures and therefore NOx emissions. Efficiency is increased and higher output is reached while avoiding knocking. Combustion of the lean air-fuel mixture is initiated by injecting a small amount of LFO (pilot fuel) into the cylinder. The pilot fuel is ignited in a conventional diesel process, providing a high-energy ignition source for the main engine. To obtain the best efficiency and lowest emissions, every cylinder is individually controlled to ensure operation at the correct air-fuel ratio and with the correct amount and timing of pilot fuel rejection. Wartsila has developed a special electronic control system to cope with the demanding task of controlling the combustion in each cylinder, and to ensure optimal performance in terms of efficiency and emissions under all conditions by keeping each cylinder within the operating window. Stable and well-controlled combustion also contributes to less mechanical and thermal load on the engine components. Current stringent emission regulations demand the reduction of NOx emissions. In an internal combustion engine this means controlling peak temperature and residence time, which are the main parameters governing NOx formations. In the Wartsila 50DF engine, the air-fuel ratio is very high (typically 2.2). Since the same specific heat quantity released by combustion is used to heat up a larger mass of air, the maximum temperature and consequently NOx formation are lower. The mixture is uniform. throughout the cylinder since the fuel and air are premixed before introduction into the cylinders, which helps to avoid local NOx formation points within the cylinder. Benefiting from this unique feature, NOx emissions from the Wartsila 50DF are extremely and comply with the most stringent existing legislation.

What is the combustion feature of the Wartsila 50DF?

A.Lean air in the cylinder

B.Excessive fuel in the cylinder

C.Excessive air in the cylinder

D.Spark ignition

Which of the following statement（s）is/are FALSE regarding a twin pedestal crane set ________．

A.The cranes may be operated independently

B.The cranes may be interconnected for twin operation

C.The cranes are powered by independent internal combustion power units

D.All of the above

A. CD-RW

B. CD-R

C. DVD-RW

D. Flash